|  | 4.2 | Network Design Methodology
| 4.2.2 | Factors that affect network availability

Availability measures the usefulness of the network. Many things affect availability, including the following: Throughput Response time Access to resources Every customer has a different definition of availability. For example, there may be a need to transport voice and video over the network. However, these services require more bandwidth than is available on the network or backbone. You can increase availability by adding more resources, but resources drive up cost. Network design seeks to provide the greatest availability for the least cost. After considering availability, the next step in designing a network is to analyze the requirements of the network and its users that were gathered in the last step. Network user needs constantly change. For example, as more voice- and video-based network applications become available, the pressure to increase network bandwidth will become intense. Another component of the analysis phase is assessing the user requirements. A LAN that is incapable of supplying prompt and accurate information to its users is of little use. Therefore, you must take steps to ensure that the information requirements of the organization and its workers are met.
| Threaded Case Study
Washington Project: Availability

Find out what availability means to your customer. In the case of the Washington School District, you need to conduct a detailed analysis of current and projected needs in order to help meet this need. Analysis of network requirements includes analyzing the district's business and technical goals. You need to answer the following questions:

- What applications will be implemented?
- What new networks will be accessed?
- What are the success criteria?
- What level of reliability must the WAN and LANs have?
- How can you tell if the new design is successful?

Threaded Case Study
Washington Project: Determining Network Traffic Load

You need to determine the network traffic load for the Washington School District before developing a network structure and acquiring hardware. Additionally, when analyzing the district's technical requirements, you should estimate the traffic load caused by applications in packet size (for example, you need to estimate the size of files in bytes per second needed to be transmitted over the network).

Certain types of network use can generate large volumes of traffic and, therefore, can cause congestion, including congestion of the following:

- Internet access
- Computers loading software from a remote site
- Anything that transmits images or video
- Central database access
- Department file servers

You should estimate worst-case traffic load on the network during the busiest times for users and during regularly scheduled network services, such as file server backups.